Good format for character mesh & animation export?
I've had marginal success with the DirectX exporter.

The DirectX format supports meshes, vertex normals, UV coordinates, simple materials, bones, bone animation, and multiple animations in the same file. I've been able to export game-ready models using this format and load them into other software with Assimp.

Unfortunately, the 'Coordinate System' and 'Up Axis' options give unexpected results, doing really strange things to the Matrix Transforms for each bone in an armature. In other words, your model may import sideways or mirrored.

Blender version 2.71 includes an updated FBX exporter (now exports to FBX v7.4 binary instead of v6.1). FBX also handles all of the above features, and is generally the format of choice when exporting animation to Unity. The drawback of FBX is that it is not yet supported by Assimp.